Drug use may be conceptualized as an impulsive choice because the user prefers the small immediate reinforcing consequences of taking drugs (e.g., getting high) over the large-delayed reinforcing consequences of drug abstinence (e.g., occupational success, improved interpersonal relations, etc.). Several studies have illustrated that drug-dependent individuals discount the value of delayed reinforcers more than non-drug- users. In these studies, psychometric techniques are used to determine the subjective value of a series of large-delayed rewards (e.g. $1,000 delivered in 1 year.) A shortcoming of this conceptual model is that the large-delayed benefits of abstinence are rarely given in a lump sum after a single delay. Instead, these benefits are typically distributed in smaller amounts over several delays (e.g., slightly improved relations with a spouse seen daily over many years). Thus, the first aim of the proposed study is to compare discounting rates across situations in which the large- delayed reinforcer is delivered in a lump sum following a single delay or delivered in smaller amounts following a series of delays. A 2 x 2 mixed factorial design will be used in which diagnosis (drug dependent vs. non- drug user) is a between-subjects factor and choice situation )delayed rewards delivered in a lump sum vs. distributed over time) is a whin- subjects factor. The second aim of the proposed study is to explore the relation between the discounting of delayed and high-priced rewards. Several studies have recently suggested that animals and humans discount high-priced rewards in a manner similar to the way they discount the value of delayed rewards available at a range of prices (price operationalized as effort required to obtain each reward). The correlation between price elasticity of demand (a measure of sensitivity to price increases) and discounting rates of individual participants will be assessed.